U.S. patent application number 12/898816 was filed with the patent office on 2012-04-12 for structure and method for mounting a photovoltaic material.
Invention is credited to Jonathan Call, Uday Varde.
Application Number | 20120085391 12/898816 |
Document ID | / |
Family ID | 45924170 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120085391 |
Kind Code |
A1 |
Varde; Uday ; et
al. |
April 12, 2012 |
STRUCTURE AND METHOD FOR MOUNTING A PHOTOVOLTAIC MATERIAL
Abstract
A photovoltaic device is adhesively mounted to a support
structure such as a roofing member or building panel by the use of
a body of foamed adhesive. The foamed adhesive is resilient and
accommodates differences in the thermal expansion and contraction
of materials comprising the photovoltaic device and the structure
upon which it is mounted and thereby prevents delamination and
other stress-related damage to the photovoltaic installation. The
adhesive may comprise a contact adhesive, a hot melt adhesive, or a
curable adhesive. Further disclosed are methods for affixing
photovoltaic systems to building structures and the like through
the use of foamed adhesives.
Inventors: |
Varde; Uday; (West
Bloomfield, MI) ; Call; Jonathan; (Royal Oak,
MI) |
Family ID: |
45924170 |
Appl. No.: |
12/898816 |
Filed: |
October 6, 2010 |
Current U.S.
Class: |
136/251 ;
29/428 |
Current CPC
Class: |
Y10T 29/49826 20150115;
Y02E 10/50 20130101; Y02B 10/20 20130101; H02S 20/23 20141201; Y02B
10/12 20130101; H01L 31/049 20141201; Y02B 10/10 20130101 |
Class at
Publication: |
136/251 ;
29/428 |
International
Class: |
H01L 31/048 20060101
H01L031/048; H01L 31/18 20060101 H01L031/18; E04D 13/18 20060101
E04D013/18 |
Claims
1. An adhesively affixable photovoltaic member comprising: a
photovoltaic device including a body of a photovoltaic
semiconductor material which operates to absorb incident photons
and generate an electrical current in response thereto, said
photovoltaic device further including a substrate having said body
of photovoltaic semiconductor material supported upon a first face
thereat and a body of a foamed adhesive supported on a second face
of said substrate opposite said first face; wherein said foamed
adhesive is operative to bond said photovoltaic device to a support
member while accommodating the differential thermal expansion of
said photovoltaic device and said support member.
2. The photovoltaic member of claim 1, wherein said foamed adhesive
is a contact adhesive.
3. The photovoltaic member of claim 1, wherein said foamed adhesive
is a curable adhesive.
4. The photovoltaic member of claim 1, wherein said adhesive is a
hot melt adhesive.
5. The photovoltaic member of claim 1, further including a
removable body of a release material adhered to said adhesive
layer.
6. The photovoltaic member of claim 1, wherein the void volume of
said foamed adhesive is in the range of 5-80 percent.
7. The photovoltaic member of claim 6, wherein said void volume is
in the range of 40-50 percent.
8. The photovoltaic member of claim 1, wherein said foamed adhesive
has an at least partially closed cellular structure.
9. The photovoltaic member of claim 8, wherein foamed adhesive has
a partially closed cellular structure in which the void volume of
the closed cells is in the range of 10% to 40%
10. The photovoltaic member of claim 1, wherein the foamed
structure of said adhesive is provided by a plurality of gas
bubbles dispersed therein.
11. The photovoltaic member of claim 10, wherein said gas bubbles
comprise a gas selected from the group consisting of: air,
nitrogen, argon, helium, a fluorocarbon, and combinations
thereof.
12. The photovoltaic member of claim 1, wherein the foamed
structure of said adhesive is defined by a plurality of hollow
microspheres dispersed therein.
13. The photovoltaic member of claim 1, wherein said body of foamed
adhesive has a thickness of at least 0.5 millimeters.
14. The photovoltaic member of claim 1, wherein said photovoltaic
device comprises a body of a thin film semiconductor material and
said substrate comprises a metal.
15. The photovoltaic member of claim 1, wherein said photovoltaic
device includes a transparent encapsulant layer disposed on a
light-incident side of said photovoltaic device.
16. The photovoltaic member of claim 1, wherein said substrate
includes a layer of an encapsulant material covering the second
face thereof, and wherein said body of foamed adhesive is disposed
atop said layer of encapsulant material.
17. A photovoltaic installation comprising: a support member; at
least one photovoltaic device; and a foamed adhesive which
adhesively affixes said at least one photovoltaic device to said
support member.
18. The photovoltaic installation of claim 17, wherein said support
member is a building structure.
19. The photovoltaic installation of claim 17, wherein said support
member is a roofing membrane.
20. A method for affixing a photovoltaic device to a support
member, said method comprising adhesively affixing said
photovoltaic device to said support member with a body of a foamed
adhesive.
Description
FIELD OF THE INVENTION
[0001] This invention relates, generally, to photovoltaic devices.
More particularly, the invention relates to a power generating
photovoltaic member which is capable of being adhesively affixed to
a building structure or the like and which accommodates the
differential thermal expansion and contraction of the building
structure and the photovoltaic material.
BACKGROUND OF THE INVENTION
[0002] The use of photovoltaic devices as large-scale sources of
electrical power is increasing owing to improvements in the
efficiency and power/weight ratio of such devices, as well as to
production efficiencies which have lowered their costs.
Photovoltaic installations typically occupy relatively large areas;
hence, roofs, upper story walls, and other unused areas of building
structures with exposure to solar irradiance, are often employed to
support photovoltaic power installations. Any such installation
should be resistant to environmental conditions including wind
loading, temperature variations, and the like. Additionally, the
installation should be light in weight and easy to install and
remove. In a number of instances, photovoltaic devices are mounted
onto roofing membranes, wall structures, and the like through the
use of adhesive materials, and such installations are shown in U.S.
Pat. Nos. 6,729,081 and 6,553,729, the disclosures of which are
incorporated herein by reference.
[0003] It has been found that in those instances where relatively
large area photovoltaic members are mounted onto building
structures, even small mismatches in the thermal expansion
coefficients of the photovoltaic material and the surface upon
which that material is mounted can result in the creation of
relatively large stresses which can delaminate cells, cause
buckling within or between cells, and/or short the photovoltaic
layers or otherwise damage the photovoltaic installation. The
present invention has recognized a source of such stresses and, as
will be described in detail hereinbelow, has developed a solution
to this problem based upon the use of foamed adhesive materials
which are capable of accommodating differential thermal expansions
while still retaining the integrity of the adhesive bond. Details
of the invention will be apparent from the drawings, discussion,
and description which follow.
BRIEF DESCRIPTION OF THE INVENTION
[0004] Disclosed is an adhesively affixable photovoltaic member
which includes a photovoltaic device having a body of photovoltaic
semiconductor material winch operates to absorb incident photons
and generate an electrical current in response thereto. The
photovoltaic device further includes a substrate having the body of
photovoltaic semiconductor material supported on a first surface of
the substrate. The photovoltaic member further includes a body of a
foamed adhesive disposed on a second surface of the substrate
opposite the first surface. The foamed adhesive is operative to
bond the photovoltaic device to a support member while
accommodating the differential thermal expansion of the
photovoltaic device and the support member. The foamed adhesive may
include but is not limited to; a contact adhesive, a thermoplastic
adhesive, a thermoset adhesive or a hot melt adhesive that can be
thermoplastic or thermoset. In specific instances, the foamed
adhesive has a void volume in the range of 5-80 percent, and in
specific instances 40-50 percent. The foam may have an at least
partially closed cellular structure, and the voids may be formed by
gas bubbles or hollow microspheres. In some instances, the body of
adhesive includes a layer of release material affixed to it.
[0005] Also disclosed is a photovoltaic installation in which a
photovoltaic device is affixed to a support member such as a roof
structure through the use of a foamed adhesive. Further disclosed
is a method for affixing photovoltaic devices to support structures
through the use of a foamed adhesive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a cross-sectional view of a portion of a first
embodiment of an adhesively affixable photovoltaic member; and
[0007] FIG. 2 is a cross-sectional view of a portion of another
embodiment of an adhesively affixable photovoltaic member.
DETAILED DESCRIPTION OF THE INVENTION
[0008] In general, the present invention comprises the use of a
foamed adhesive material to bond photovoltaic devices to support
structures such as roofing membranes, building panels, and the
like. The foamed adhesive provides elasticity to the bond which
allows the installation to accommodate stresses and strains
resultant from the differential thermal expansion and contraction
of the various components of the photovoltaic material and the
underlying support structure to which it is bonded. This invention
may be implemented in a variety of embodiments utilizing various
foamed adhesives and various configurations of photovoltaic device.
The invention will be explained with reference to some very
specific embodiments, and it is to be understood that these
embodiments are illustrative of the general principle, and the
invention may be otherwise implemented.
[0009] Referring now to FIG. 1, there is shown a cross-sectional
view of a photovoltaic member 10 in accord with the present
invention. The member 10 includes a photovoltaic device shown
generally at reference numeral 12. The photovoltaic device includes
a photovoltaic semiconductor body 14 which includes one or more
semiconductor layers and which operates to absorb incident photons
and generate an electrical current in response thereto. In one
specific embodiment of the present invention, the photovoltaic body
14 includes a plurality of thin film semiconductor layers such as
amorphous and/or microcrystalline layers of alloys of hydrogenated
silicon and/or germanium. However, it is to be understood that
other semiconductor materials such as cadmium telluride, cadmium
sulfide, and the like may be also utilized in the practice of the
present invention, as may be single crystal and polycrystalline
materials. As is known in the art, the photovoltaic body 14 may
include current collecting electrode structures, protective layers,
current buffer layers, and the like. As is further shown in FIG. 1,
the photovoltaic device 12 includes a substrate material 16 having
the body of photovoltaic semiconductor material 14 supported on a
first face thereof. As shown in FIG. 1, this body 14 is supported
directly upon the first face of the substrate 16, although it is to
be understood that additional layers such as reflective layers,
optical tuning layers, texture layers, and the like may be
incorporated either into the substrate or be disposed between the
substrate 16 and the semiconductor body 14. In some specific
instances, the substrate 16 may be a metallic substrate which may
additionally function as a component of the bottom electrode of the
photovoltaic device. In other instances, the substrate 16 may
comprise a layer of polymeric material.
[0010] As further shown in FIG. 1, a layer of a foamed adhesive
material 18 is supported on a second face of the substrate 16. In
this instance, the adhesive material 18 is supported directly on
the second face of the substrate 16, although it is to be
understood that additional layers such as reinforcement layers and
the like may be interposed therebetween.
[0011] The foamed adhesive 18 is characterized in that it includes
a plurality of voids, also referred to as cells, defined therein.
In particular instances, the combined volume of these voids,
referred to as the "void volume" of the adhesive, will be in the
range of 5-80 percent. That is to say, of the total volume of the
adhesive, 5-80 percent of the volume will be constituted by the
voids. In specific instances, void volumes of 40-50 percent are
utilized in the practice of the present invention. It has been
found that the presence of the voids in the adhesive enhances the
resilience and elongation of the adhesive under stress and this
resiliency allows the foamed adhesive to accommodate dimensional
discrepancies between the photovoltaic device and an underlying
substrate to which it is bonded. In addition to providing
accommodation for the thermal expansion and contraction, the foamed
adhesive layer also significantly decreases the weight of the
adhesive material without decreasing the area of contact between
the adhesive and the surface to which it is affixed; therefore, the
foamed adhesive allows for the use of a thicker adhesive body
and/or a decreased amount of adhesive as compared to systems
utilizing nonfoamed adhesives.
[0012] In particular instances, the voids are formed in the
adhesive by bubbles of gas dispersed therein. There are a number of
gases which may be utilized to prepare the foamed adhesives, and
such gases can include air, nitrogen, argon, xenon, or other noble
gases as well as hydrocarbons or halocarbons such as chlorocarbons,
fluorocarbons and the like. In some instances the foaming may be
accomplished by the use of chemical compounds which decompose to
release a gas, typically nitrogen. Such agents include
Azobisformamide type compounds and the like. In other instances,
the foam structure may be provided by dispersing hollow
microspheres such as glass or polymeric microspheres in the
adhesive. Such microspheres are known and readily available to
those of skill in the art.
[0013] Various adhesives may be used to prepare the foamed adhesive
layer, and such adhesives include acrylics, urethanes, silicones,
elastomeric compounds such as EP rubbers, butyl rubbers, and the
like. Photosensitive adhesives such as UV tackifiable PSA adhesives
comprise polymeric materials which can be applied to a surface as a
relatively low viscosity resin and subsequently tackified by
exposure to ultraviolet radiation so as to convert them to a
contact adhesive material; and, such materials may also be used as
a basis for the foamed adhesive.
[0014] As is shown in FIG. 1, a release layer 20 may be applied to
the adhesive layer 18 so as to protect it during shipping and
handling. This release layer 20 may comprise a layer of paper or
polymeric material coated with a release coating of a silicone or
the like and its inclusion has been found particularly advantageous
in those instances where the adhesive layer 18 is a contact
adhesive.
[0015] In some instances, the present invention may be implemented
utilizing curable adhesives. Such adhesives include chemically
curable adhesives as well as optically curable and thermally
curable adhesives. In yet other instances, the adhesive may
comprise a hot melt adhesive. Use of curable and hot melt adhesives
may confer particular advantages in those instances where the
photovoltaic members are being affixed to support structures in a
manufacturing situation or in a high volume onsite installation
system. Contact adhesives will often be found to be advantageously
employed in those situations in which worksite application or
consumer application of the devices is anticipated.
[0016] Referring now to FIG. 2, there is shown another embodiment
22 of photovoltaic member in accord with the principles of the
present invention. In this embodiment, the photovoltaic device
portion is comprised of a substrate 16 which can be generally
similar to the previously described substrate and is further
comprised of two photovoltaic bodies 24 and 26 disposed on the
substrate 16. In this instance, the photovoltaic bodies 24 and 26
may each comprise discrete photovoltaic cells, or arrays of such
cells. As such, each body 24, 26 will include semiconductor layers,
electrodes, and substrates; and in particular instances, the
individual photovoltaic bodies 24 and 26 may be interconnected in a
series or parallel relationship to form a module as is known in the
art. In the FIG. 2 embodiment, the substrate 16 and photovoltaic
bodies 24 and 26 are encapsulated in an encapsulant material 28
which, in this embodiment, covers the entirety of the bodies 24 and
26 as well as the substrate 16. In other embodiments, the
encapsulant may cover only the photovoltaic bodies 24 and 26 and
upper surface of the substrate 16. As is known in the art, such
encapsulants will typically comprise polymeric materials and will
be light transparent at least with regard to that portion thereof
which covers the light-incident side of the photovoltaic bodies. In
the FIG. 2 embodiment, a layer of foamed adhesive 18 is disposed so
as to be supported by the second surface of the substrate 16, which
in this case further includes the intervening portion of the
encapsulant 28. The FIG. 2 embodiment, like the FIG. 1 embodiment,
may also include an optional release layer, although such layer is
not shown in FIG. 2.
[0017] Various techniques may be employed for preparing the foamed
adhesive layers. As described above, foaming may be accomplished by
introducing a gas into the adhesive, and systems for doing so are
commercially available from a number of suppliers including the
Nordson Corporation of Duluth, Ga. In other instances, foaming may
be accomplished by incorporating a chemical foaming agent into the
adhesive mixture. Such foaming agents include chemically reactive
compounds such as azides which decompose to release nitrogen, as
well as vaporizable agents such as hydrocarbon or
chlorofluorocarbon blowing agents which volatilize to produce
bubbles in the adhesive. As previously noted, foaming may also be
accomplished by mixing hollow microspheres of glass or polymer into
the adhesive to create voids. As is known in the art, the foaming
of the adhesive may produce an open-cell structure in which the
voids are in communication with one another. The foaming may
alternatively produce a closed-cell structure in which the interior
of each of the voids is essentially separate from the others. In
yet other instances, a mixed open-cell/closed-cell structure may be
produced. All of such structures may be used in the practice of the
present invention. In general, open cell structures have greater
elasticity than do closed cell structures, while closed cell
structures are less permeable to moisture than are open cell
structures. Thus, by controlling the ratio of closed cells to open
cells in the adhesive structure, properties of the adhesive may be
advantageously controlled. In roofing installations and other
situations where good moisture resistance is required, the closed
cell void volume of the foam should be at least 10%; however, in
order to provide sufficient elasticity to the foam, the open cell
void volume should be at least 30%. In a typical installation,
where moisture resistance is required, the closed cell void volume
of the foam will be in the range of 10% to 40%, and in specific
instances, the closed cell void volume will be in the range of 10%
to 25%.
[0018] In particular instances, the foamed adhesive may be directly
applied to the photovoltaic structure either at the time of
fabrication, or at the time the photovoltaic material is to be
adhered to the support structure. In other instances, the foamed
adhesive may be cast into a sheet member that is further processed
and then adhered to the photovoltaic device and/or support
structure. In yet other instances, the adhesive may be applied to
the support structure and the photovoltaic device placed thereupon.
All of such modes of application are contemplated within the scope
of this disclosure. Various techniques may be employed for coating
the adhesive. In some instances, a single apparatus may be used for
foaming and dispensing the adhesive. In other instances, the
adhesive may first be foamed, and then coated; while in yet other
instances, foaming may be accomplished after coating, as for
example by the use of foaming agents.
[0019] The thickness of the adhesive layer will depend upon the
nature of the adhesive as well as the size, weight, and orientation
of the photovoltaic device. However, in typical installations, the
adhesive layer will have a thickness of at least 0.5 millimeters,
and in more particular instances a thickness of approximately 1
millimeter or more. While thinner layers may be employed, the
thickness should be selected such that sufficient flexibility and
resilience will be achieved at the adhesive joint so as to
accommodate differential expansion of the materials. While foamed
adhesives are known in the art, the advantages and benefits
dependent upon their use in connection with the installation of
large area photovoltaic power systems has not been heretofore
appreciated.
[0020] The foregoing describes some specific embodiments of the
present invention. Yet other embodiments, modifications, and
variations will be apparent to those of skill in the art in view of
the teaching presented herein, and all of such embodiments,
modifications, and variations are within the scope of the present
invention. It is the following claims, including all equivalents,
which define the scope of the invention.
* * * * *